Steerable stylet

ABSTRACT

A steerable stylet for use within a lumen of an intravascular device includes a stylet assembly and a handle. The stylet assembly has a distal end portion and a proximal end portion and includes a stylet wire having a lumen and a core wire positioned within the lumen with the distal end portion secured to the stylet wire proximate the distal end portion of the stylet wire. The handle includes a hand-held housing structure connected to one of the proximal end portion of the stylet wire or the core wire. In one embodiment, an adjustable tensioner is connected to the other of the proximal end portion of the stylet wire or the core wire to adjust a relative tension force applied between the stylet wire and the core wire. A tension limiter is arranged to limit the tension force to a limit force that is less than a breaking stress force of the stylet wire when the stylet wire is positioned within the lumen of the intravascular device. In another embodiment, a plurality of notches are defined in one or more regions of the distal portion of the tubular stylet wire to aid in the safe and effective creation of large and/or compound curves. Preferably, the core wire is secured within the tubular stylet wire without heating the either wire so as to prevent any annealing of the materials that would decrease the tensile strength of the distal end portion of the stylet.

FIELD OF THE INVENTION

[0001] The present invention relates generally to the field ofintravascular leads and catheters. More specifically, the presentinvention relates to steerable stylet for use in positioning such leadsand catheters.

BACKGROUND OF THE INVENTION

[0002] Stylets and guidewires are used to control the manner in whichintravascular leads and catheters are introduced into the veins orarteries of the body. Although both kinds of devices are often thoughtof as simply very small wires, the purpose and operation of stylets issignificantly different as compared to guidewires.

[0003] Conventional intravascular procedures typically involve aninitial step of introducing and routing a guidewire through a patient'svascular system to provide a rail or track along which additionalintravascular devices may be introduced. Once a guidewire is in place, asheath is routed over at least a portion of the guidewire to provide alarger opening into the vein or artery and sometimes to protect theinside walls of the vessels along the route of the guidewire. With thesheath in place, the guidewire may be removed or may remain in place asadditional intravascular devices, such as intravascular leads andcatheters, are introduced into the patient's vascular system.

[0004] To better accomplish the purpose of a guidewire providing a trackalong the patient's vascular system for other intravascular devices, itis desirable that the guidewire be extremely flexible and preferablyhave the ability to vary the flexibility of the distal tip and/ordeflect the distal tip so as to aid in routing the guidewire through thepatient's vascular system. U.S. Pat. Nos. 4,215,703, 4,456,017,4,719,924, 4,757,827, 4,886,067 and 5,060,660 describe designs forguidewires that use an internal tensioning member or core wire to alterthe characteristics of the non-expandable distal tip and/or to deflectthe distal tip. U.S. Pat. Nos. 4,271,845 4,822,345, 5,605,162,5,762,615, 5,851,203, 5,957,903 and 6,183,420 describe various designsfor guidewires with adjustable stiffness by moving a core member axiallywithin the guidewire. U.S. Pat. Nos. 5,938,623 and 6,039,743 describe aguidewire with adjustable stiffness that is controlled by runningelectricity through a memory metal wire tip. Flexibility of theguidewire has also been provided by gradually tapering some portion ofthe distal end as described in U.S. Pat. Nos. 5,851,203 and 5,916,178 orby changing materials at the end of the guidewire as described in U.S.Pat. Nos. 6,017,319 and 6,068,623. The flexibility of guidewires hasalso been enhanced by making cuts or slots in the distal region of theguidewire as shown in U.S. Pat. Nos. 3,802,440, 5,437,288, 5,605,543,5,833,632, 6,004,279 and 6,017,319. Similar arrangements for increasingthe flexibility of the catheter that is tracked over the guidewire arealso described in U.S. Pat. Nos. 5,304,131, 5,315,996, 5,322,064,5,441,483, 5,573,520, 5,743,876 and 6,048,339. Catheter arrangementscapable of producing compound bends are described in U.S. Pat. Nos.5,758,656 and 5,820,591.

[0005] In contrast to the guidewire that serves as a track over whichother intravascular devices are routed, a stylet is used within aninternal lumen of an intravascular device both to push that devicethrough the vascular system and to steer the device as it is beingpushed. Although some intravascular devices are designed to steerthemselves using internal core wires, almost all leads, most cathetersand some guidewires have an inner channel or lumen into which a styletis inserted. In addition to pushing the intravascular device through thevascular system by engaging the distal end of the device, the styletalso serves to deflect the distal end of the intravascular device so asto steer the distal end through the vascular system. Unlike the lead,catheter or guidewire, which is highly flexible and floppy, the styletmust be stiffer and more rigid so as to enable the stylet to push thelead or catheter through the patient's vascular system. In addition,guidewires have diameters that are typically at least twice as large(0.030-0.040 inches) as the diameters of stylets (less than 0.016inches) because guidewires are most often formed of a coiled wire,instead of a straight tubular wire.

[0006] Conventionally, stylets having different bends on the distal endare used at different points of advancing the lead or catheter to adesired location. For straight segments of a vessel a straight stylet isused, whereas a stylet with a curved distal tip is used to navigate thelead or catheter through a curved portion of a vessel. U.S. Pat. No.2,118,631 shows an early stylet formed of coils of flat wire welded toplugs at both ends that could be bent by the physician into either astraight or curved configuration at its distal end prior to insertioninto the lumen of a catheter or the like. U.S. Pat. Nos. 4,498,482 and4,796,642 show early examples of solid wire stylets. While suchconventional stylets can be used effectively in the hands of a skilledsurgeon, the process can be complicated and time consuming. Implantationof a lead with a conventional stylet often involves multiple insertionsand withdrawals of the stylet, with the surgeon adjusting the bend onthe distal end so as to be able to continue to advance the stylet andlead into a desired position. One type of lead placement that isparticularly complicated is the placement of a J-shaped lead in theatrial chamber. In this procedure, a straight stylet is used to advancethe lead into the atrial chamber of the heart. Once there, a J-shapedstylet is used to force the lead to bend back on itself in order to besecured in a desired location in the atrium.

[0007] To overcome the problem of having to repeatedly insert andwithdraw a stylet in order change the shape of the distal end, attemptshave been made to develop a steerable stylet. In a steerable stylet anoperator uses a handle at the proximal end of the stylet to control thedirection of deflection of the distal tip of the stylet while it is inplace in the lumen of the lead or catheter as it is moved along theveins or arteries. Typically, a steerable stylet is arranged as a styletwire having a lumen within which a core wire is positioned with thedistal ends of the two wires being attached. The handle is used tocreate a differential tension between the core wire and the stylet wireso as to deflect the distal end of the stylet as a result. Examples ofsuch steerable stylets with deflectable tips are shown in U.S. Pat. Nos.4,209,019, 5,396,902, 5,439,006, 5,662,119, 5,674,271, 5,824,031,5,873,842, 6,027,462, 6,059,739, and 6,203,506. Other examples ofsteerable stylets can be found in PCT Publ. No. WO 00/22981 andpublications describing the Placer™ steerable stylet and the Locator™steerable stylet.

[0008] In U.S. Pat. No. 5,752,915, a steerable stylet uses an operatingslide to retract a stylet sleeve that is not attached to the stylet wireso as to selectively expose a pre-bent distal portion of a stylet wireto deflect the distal end of an electrode lead. The handle of thisstylet includes a spring for the purpose of enclosing the proximal endof the stylet wire in a tight brace to prevent buckling of the styletwire due to friction between the stylet wire and the stylet sleeve asthe stylet sleeve is retracted. In U.S. Pat. No. 5,327,906, a stressrelief sleeve is provided at the junction of the stylet wire and a nosecone for the handle that allows the stylet to be removably mounted inthe handle. A stop pin is also used to limit the rearward travel of aslide for the purpose of controlling the degree of curvature of thedistal end of the stylet by using the stop pin to change the length ofthe slide. In U.S. Pat. No. 6,132,390, a conical tip is also provided tominimize stress on the stylet. A flexible plastic or polymeric jacket isdisposed over the stylet wire to prevent kinking or catastrophicinelastic failure of the distal tip under a radial load.

[0009] While the advantages of a steerable stylet are apparent, none ofthe existing designs for steerable stylets has achieved widespreadacceptance. One of the principle challenges in designing an effectivesteerable stylet is creating a robust design that enables a largecurvature of the distal end, preferably more than 120° so as toaccommodate placement of J-shaped leads or alternatively creatingsigmoidal or compound bends, while at the same time providing theflexure strength to permit repeated bending of the stylet withoutfracture or breaking. Unlike guidewires or catheters, these designconsiderations must be developed to operate under conditions where thestylet is within and constrained by the lumen of the lead or catheterthat is being implanted. It would be desirable to provide a steerablestylet that could overcome these challenges and provide a robust designcapable of large or compound curvatures that safely allows for repeatedbending of the stylet without fracture or breaking.

SUMMARY OF THE INVENTION

[0010] The present invention provides a steerable stylet for use withina lumen of an intravascular device. The stylet includes a styletassembly and a handle. The stylet assembly has a distal end portion anda proximal end portion and includes a tubular stylet wire having a lumenand a core wire positioned within the lumen with the distal end portionsecured to the stylet wire proximate the distal end portion of thestylet wire. Unlike a conventional guidewire, the stylet wire hasdiameter of less than 0.016 inches and a beam strength of at least 0.005lbf as measured by the ASTM E855-90 3-point bend test. The core wire hasa distal end portion and a proximal end portion and is positioned withinthe lumen of the stylet wire with the distal end portion secured to thestylet wire proximate the distal end portion of the stylet wire. Thehandle includes a hand-held housing structure connected to one of theproximal end portion of the stylet wire or the core wire. In oneembodiment, an adjustable tensioner is connected to the other of theproximal end portion of the stylet wire or the core wire to adjust arelative tension force applied between the stylet wire and the corewire. A tension limiter is arranged to limit the tension force to alimit force that is less than a breaking stress force of the stylet wirewhen the stylet wire is positioned within the lumen of the intravasculardevice. In another embodiment, a plurality of notches are defined in oneor more regions of the distal portion of the tubular stylet wire to aidin the safe and effective creation of large and/or compound curves.Preferably, the core wire is secured within the tubular stylet wirewithout heating either wire so as to prevent any annealing of thematerials that would decrease the tensile strength of the distal endportion of the stylet.

[0011] By limiting the tension force that can be applied between thecore wire and the stylet wire to a force that is less than the breakingstress force of the stylet wire, the present invention prevents thestylet wire from failing as a result of an excessive stress force. Thisprevents an operator from overexerting the stylet wire by attempting todeflect the stylet in a situation where the intravascular device cannotbe deflected, such as for example within a blood vessel. Unlike a designthat provides for a fixed dimensional travel of the adjustabletensioner, the present invention provides for a floating or variableamount of travel up to a maximum deflection force. As a result, thestylet may be repeatedly deflected numerous times without causing eithera stress or fatigue failure of the stylet wire. In one embodiment, thesteerable stylet of the present invention is designed for implantationof cardiac J-leads and can be deflected up to a maximum deflection of atleast 180° from an original position of the stylet wire and thedeflections can be repeated at least fifty times without inducing stressor fatigue failure in the stylet wire. In another embodiment, thesteerable stylet of the present invention is designed for use inneurological applications and can be deflected up to a maximum of 90°and can also be configured to create compound curves.

[0012] In a preferred embodiment, a series of at least ten notches aredefined along a distal region of the stylet wire to prevent the stressesinduced in the distal region of the stylet wire from kinking or bendingthe stylet when the distal end portion of the stylet is deflected by anoperator. Preferably, the series of notches in the distal regionincludes at least a portion of the notches that have a progressivelydecreasing depth distally to proximally along the series. Morepreferably, the portion of the notches having a progressively decreasingdepth has a constant decrease in depth between adjacent notches. In thisembodiment, the distal region is preferably defined beginning between0.050 inches and 1.000 inches proximal to the distal end of the styletwire. Preferably, there are at least twenty-five notches of between0.005 inches and 0.015 inches longitudinal width with a spacing betweenadjacent notches of between 0.010 inches and 0.050 inches and a depth ofat least ten of the most distal notches of said series beingapproximately equal to a radius of the stylet wire minus a wallthickness of the stylet wire. In an alternate embodiment, more than oneseries of notches are defined in the distal region of the stylet wire tocreate compound curves, including curves oriented in two differentplanes. Preferably, the spacing and dimensions of the notches aredifferent between the different series so as to stage the sequence inwhich each region associated with a given series of notches will inducea curve in response to tension on the core wire.

[0013] In a preferred embodiment, the proximal end portion of the corewire is fixedly connected to the adjustable tensioner and the tensionlimiter has a first end portion fixedly connected to the housingstructure of the handle and a second end portion operably connected tothe adjustable tensioner. Preferably, the breaking stress force of thestylet wire is at least six pounds and the limit force of the tensionlimiter is less than four pounds. In one embodiment, the tension limiteris a constant force spring. In another embodiment, the tension limiteris an elastomer member with a maximum compressive retention force lessthan the breaking stress force of the stylet wire.

[0014] Preferably, the core wire is secured within the tubular styletwire without heating either wire so as to prevent any annealing of thematerials that would decrease the tensile strength of the distal endportion of the stylet. In one embodiment, the core wire is taper groundto provide a smaller diameter core shaft while leaving a bulbous distalend having a diameter substantially equal to an outer diameter of thetubular stylet wire. The core wire is slide into the lumen of thetubular stylet wire and the bulbous distal end of the core wire issecured in place using adhesives together with a chamfered fit. Byavoiding the use of heat for welding or thermal expansive fits, the corewire and stylet wire are not annealed and the corresponding decrease intensile strength of the wires (to about 60% of their original tensilestrength) is not encountered.

[0015] In one embodiment, the handle includes a mechanism for providingtactile psuedo-feedback to an operator that is generally indicative ofthe relative tension force without directly engaging the tensionlimiter. In another embodiment, the beam strength of the stylet wire ispreferably about 0.010 lbf so as to be sufficient to cause the styletwire to return to at least an original position as the relative tensionforce is removed from the stylet wire and preferably to an angle beyondits original position.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is a perspective view illustrating the steerable stylet andmanipulative handle assembly of the present invention.

[0017]FIG. 2 is a perspective view of the first embodiment of themanipulative handle of the present invention in which the manipulationis controlled by sliding a thumb plate along the top of the handle.

[0018]FIG. 3 is a top view of the embodiment shown in FIG. 2.

[0019]FIG. 4 is a side view of the embodiment shown in FIG. 2.

[0020]FIG. 5 is a longitudinal cross-section of the embodiment shown inFIG. 2.

[0021]FIG. 6 is a side view of an additional embodiment of themanipulative handle of the present invention in which the manipulationis affected through turning a portion of the handle.

[0022]FIG. 7 is a top view of the embodiment shown in FIG. 6.

[0023]FIG. 8 is a perspective view of an additional embodiment of themanipulative handle of the present invention in which the manipulationis controlled by pulling or pushing the thumb hold of a three-fingerhandle.

[0024]FIG. 9 is a top view of the embodiment shown in FIG. 8.

[0025]FIG. 10 is a side view of the embodiment shown in FIG. 8.

[0026]FIG. 11 is a perspective view of an embodiment the distal portionof the stylet wire of the present invention illustrating an arrangementof notches in the stylet wire.

[0027]FIG. 12 is a detail of the notches in the distal portion of thestylet wire.

[0028]FIG. 13 is an illustration of the curvature imparted upon thestylet wire by manipulation of the handle in accordance with theteachings of the present invention.

[0029]FIG. 14 provides cross-sections of a vein containing a steerablestylet within a medical lead.

[0030]FIG. 15 is a cross-sectional view of the right atrium of apatient's heart containing a steerable stylet within a medical lead.

[0031]FIGS. 16 and 17 are isometric views of alternate embodiments ofthe tension limiting member.

[0032]FIGS. 18 and 19 are exploded views of alternate embodiments of thefront portion of the handle.

[0033]FIG. 20 is a cross-section view of an alternate embodiment of thehandle having an adjustable front portion.

[0034]FIG. 21 is a cross-section view of an embodiment of the handleincorporating a tactile psuedo-feedback mechanism.

[0035]FIGS. 22 and 23 are detailed cross-sectional views of an alternateembodiment of the stylet assembly for creating compound and sigmoidalcurves.

[0036]FIGS. 24 and 25 are side and end views of the notches in a distalportion of the stylet assembly.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

[0037] The present invention is directed to a steerable stylet 20 foruse in various intravascular medical procedures, such as cardiaccatheter procedures and neurological procedures. Although the presentinvention will be described with respect to embodiments designedspecifically for cardiac and neurological procedures, it will beunderstood that a steerable stylet 20 in accordance with the presentinvention may be used to advance and steer any kind of intravasculardevice 50 through the vascular system of a patient to a desiredtreatment location.

[0038] Referring to FIG. 1, a steerable stylet 20 in accordance with thepresent invention broadly comprises a stylet assembly 22 that includes astylet wire 24, a core wire 26, and a manipulative handle 28. Forpurposes of describing the present invention, the stylet assembly 22includes a distal end portion 30 that can be selectively deflected by anoperator through operation of the manipulative handle 28 operablyconnected to a proximal end portion 32 of the stylet assembly 22. Itwill be understood that the terms distal end portion and proximal endportion are used in the present invention to mean the longitudinal endas well as a portion proximate the longitudinal end and extendinglongitudinally back from the longitudinal end.

[0039] The stylet assembly 22 is preferably a multiple componentarrangement that includes at least the stylet wire 24 having at leastone lumen 34 defined therein with the core wire 26, sometimes referredto as a pull wire, positioned in the lumen 34. The distal end portion 36of the stylet wire is fixedly attached to the distal end portion 40 ofthe core wire. Stylet wire 24 is preferably 300 series stainless steeltubing that may be either high tensile or low tensile. Core wire 26 ispreferably 300 series stainless steel solid core wire that is preferablyhigh tensile. Alternatively, stylet wire 24 and core wire 26 can be madeof other metal alloys, such as nickel-titanium, or have a portion ofeach wire created from different material combinations (e.g., distal endportion 36 made from nickel-titanium and proximal end portion 32 madefrom stainless steel). Alternatively, core wire 26 could be made ofother metal alloys or of a filament material sufficient strong enough totransmit the relative tension force (as will be described) withoutbreaking. It should be noted that if the stylet wire 24 is welded to thecore wire 26 at the distal end portions 36, 40, one or both of the wiresmay be annealed in the welding process.

[0040] Stylet wire 24 has an outer diameter of less than 0.016 inchesand a beam strength of at least 0.005 lbf and preferably about 0.010 lbfas measured by the ASTM E855-90 3-point bend test, the specification ofwhich is hereby incorporated by reference. In contrast, conventionalfloppy tip guidewires of the same relative size have beam strengths ofless than 0.0025 lbf as measured by the ASTM E855-90 3-point bend testand more typically have beam strengths of only about 0.001 lbf. In oneembodiment, stylet wire 24 has an inner diameter of 0.008 inches andcore wire 26 has an outer diameter of 0.007 inches providingapproximately 0.0005 inches clearance within the lumen 34. The outerdiameter of less than 0.016 inches and beam strength of at least 0.005lbf effectively permit stylet assembly 22 to be used as a stylet forinsertion into a lumen 52 of an intravascular device 50, as shown forexample in FIGS. 14 and 15. Preferably, stylet wire 24 has a singlelumen 34 to permit the outer diameter to be as small as possible whilestill providing sufficient strength so as to meet the beam strengthrequirements. Alternatively, stylet wire 24 could have multiple lumensalthough for current wire technology the number and size of the lumenswill certainly impact on the beam strength and outer diameterlimitations required by the present invention. In another embodiment,the lumen 34 in which core wire 26 is located could be defined partiallyor completely external to a solid stylet wire 24 by use of collars orrings attached to the exterior of the solid wire, for example, or byproviding slots or openings in the lumen 34 of a tubular wire to allowcore wire 26 to extend beyond the outer diameter of stylet wire 24 whena relative tension force is applied between stylet wire 24 and core wire26.

[0041] The distal end portions 36 and 40 of the stylet wire 24 and thecore wire 26 are preferably fixedly secured to one another withoutheating either wire so as to prevent any annealing of the materials thatwould decrease the tensile strength of the distal end portion of thestylet, such as by making a mechanical and/or adhesive connection or bycrimping. Alternatively, the distal end portions 36 and 40 may beoperably attached to one another by welding or soldering, or anycombination of these techniques as long as the bond between the styletwire 24 and the core wire 26 is at least as strong, and preferablystronger, than the materials of the wires themselves. In one embodiment,the longitudinal ends or tips of distal end portions 36 and 40 aresecured together. Alternatively, the longitudinal tip of distal endportion 40 could be secured in the distal end portion 36 at a locationother than the longitudinal end or tip that is proximate to thelongitudinal tip.

[0042] In one embodiment as shown in FIG. 12, stylet assembly 22 alsoincludes a polymeric sheath 44 surrounding at least the distal endportion 30 of stylet assembly 22. The polymeric sheath, 44 is preferablya polyimide material. Alternatively, a Teflon® or Kapton® tubingmaterial may be used. The polymeric sheath 44 is particularly suited foran embodiment of the steerable stylet 20 intended for cardiac-relateduses where the vessels are somewhat larger and the intravascular devices50 tend to have larger inner diameters. The polymeric sheath 44 servesto protect the stylet assembly 22 from body fluids and also can reducesliding friction between the distal end portion 30 of stylet assembly 22and the lumen 52 of intravascular device 50. In a preferred embodimentfor cardiac-related uses, the stylet assembly 22, including thepolymeric sheath 44, has an outer diameter of 0.015 inches. In analternative embodiment intended for neurological uses where smallervessels are typically involved and the intravascular devices 50 tend tohave lumens smaller inner diameters, the polymeric sheath 44 is notincluded and the stylet assembly 22 has an outer diameter of 0.013inches. It will be understood that polymeric sheath 44 preferablyextends at least over a distal region 46 in which a number of notches 48are defined as will be described in connection with the description ofFIG. 12. Alternatively, polymeric sheath 44 can extend oversubstantially the entire length of stylet wire 24.

[0043] It will be realized that a variety of treatments for constructingthe distal end portion 30 of stylet assembly 22 can be utilized,depending upon the particular configuration and desired operation of thestylet assembly 22 within the intravascular device. For example, a ball,tube, or coiled spring could be added to the distal end portion 30 ofthe stylet assembly 22. Alternatively, distal end portion 30 couldinclude a structure designed to engage a distal portion 54 of theintravascular device 50, such as a flat driver structure or the like forextending and retracting a helical anchor coil located on the distal endportion 54 of the intravascular device 50.

[0044]FIG. 2 shows one embodiment of the manipulative handle 28. FIG. 5presents a cross-section of the manipulative handle 28. The manipulativehandle 28 comprises a housing 60, a tension limiting assembly 62, and anadjustable tensioner mechanism 64. In the embodiment shown in FIGS. 2and 5, the adjustable tensioner mechanism 64 is a sliding mechanism andthe tension limiting assembly 62 is a spring. The proximal end portion42 of the core wire 26 is fixedly connected to the housing structure 60.The proximal end portion 38 of the stylet wire 24 is fixedly connectedto the sliding mechanism 64. The tension limiting spring 62 has a firstend portion 66 fixedly connected to the housing structure 60 and asecond end portion 68 that is operably connected to the slidingmechanism 64. When the stylet handle 28 is activated by moving thesliding mechanism 64 in a distal direction, the stylet wire 24 movesdistally, but the core wire 26 is restricted from moving, thus creatinga relative tension force separating the core wire 26 from the styletwire 24. In the event that that activated handle 28 is operated to exerta relative tension force of more than about four lbs. of force, thesafety feature of the tension limiting spring 62 starts to open andrestricts any further load build-up of force on the proximal end portion30 of the stylet assembly 22, other than the constant force of thetension limiting spring 62 being extended.

[0045] It will be appreciated that numerous combinations of operableconnections among the proximal end portion 38 and 42 with the housing60, adjusting mechanism 64 and tension limiting member 64 can bearranged to provide for a relative tension force that separates the corewire 26 from the stylet wire 24. For example, the core wire 26 could becoupled to the sliding mechanism 64 instead of the stylet wire 24, withthe stylet wire 24 secured to the housing 60. Alternatively, one or theother of the stylet wire 24 or core wire 26 could be secured to thetension limiting member with the other operably coupled to the adjustingmechanism 64. It will also be seen that the adjusting mechanism 64 canbe made to operate in any number of arrangements, with the relativetension force created by a distal movement of the adjusting mechanism 64or, alternatively, by a proximal movement of the adjusting mechanism 64.The tension limiting spring 62 can be arranged to operate in eithercompression or tension modes, depending upon the configuration of theother connections of the proximal end portions 38 and 42 of the styletwire 24 and core wire 26 and the arrangements of the adjusting mechanism64. Multiple adjusting mechanisms 64 can be arranged so as to provide,for example, for a course adjustment with a first mechanism and a fineadjustment with a second mechanism. FIGS. 16 and 17 show two differentembodiments of tension limiting member 62. A first embodiment as shownin FIG. 16 in which tension limiting member 62 is a coil spring that isattached at each end to an engagement structure 92, 94 for engaging thetension limiting member 62 within place in the handle 60. FIG. 17 showsa second embodiment in which tension limiting member 62 is a tubularelastomeric material surrounding a compressible piston arrangement 96.It will be apparent that numerous other arrangements and configurationsof the tension limiting member and the engagement structures could beused to accomplish the purpose of limiting the force applied to thestylet wire 24.

[0046]FIG. 18 presents one embodiment of a lead locking mechanism 124that allows the manipulative handle 28 to be placed at multiplelocations along the length of the proximal end of the lead 128. The leadlocking mechanism 124 utilizes a lead clip 126 that secures the proximalend of the lead 128 to the housing 60 by gripping grooves 130 in theproximal end of the lead 128. The proximal end of the lead 128 feedsthrough a spacer 132 at the distal end of the manipulative handle 28that keeps the proximal end of the lead 128 centered within themanipulative handle 28.

[0047]FIG. 19 presents another embodiment of the lead lock lockingmechanism 124 where the proximal end of the lead 128 is threaded througha gland 134 that is in turn secured within a slot 136 at the proximalend of the manipulative handle 28. Twisting the rear portion 72 of themanipulative handle 28 provides compressive force to the gland 134,which secures the proximal end of the lead 128 within the manipulativehandle 28.

[0048]FIG. 20 shows an embodiment of the manipulative handle 28 thataccommodates variations in stylet wire 24 and core wire 26 lengths. Inthis embodiment, the lead clip 126 is at the distal end 38 of themanipulative handle 28 and secures the proximal end of the lead 128within the manipulative handle 28. The distal end 38 of the manipulativehandle 28 may be moved toward or away from the housing 60 to accommodatedifferent lengths of stylet wire 24 or core wire 26.

[0049] With reference to FIG. 21, one embodiment of the handle assembly28 is provided with a tactile psuedo-feedback mechanism 97. Although afeedback mechanism could be provided which directly engaged the tensionlimiting member of the preferred embodiment, this would tend tocomplicate the design and introduce additional forces that would need tobe accounted for in the design of the tension limiting memberarrangement. Instead, this embodiment utilizes a compression spring 98together with an engaging end 99 of sliding mechanism 64 positioned inthe front portion 74 of handle assembly 70. As the sliding mechanism 64is operated to increase actual relative tension between the stylet wire24 and the core wire 26, the engaging end 99 of the sliding mechanism 64compresses the compression spring 98, thereby creating an increasingload on the sliding mechanism 64 that can be sensed by an operatorduring operation of the device as an increasing resistance to theability to move sliding mechanism 64 forward. Preferably, thecompression spring 98 is selected to provide a tactile feedback ofincreasing force that is similar in character to the actual force curvecharacteristics that occur for the particular stylet assembly 22.Preferably, the feedback spring 98 operates in a range that provides afeedback force of 0-2 lb. It will be understood that the force offeedback spring 98 can be scaled to operate in varying ranges based onthe mechanical properties of the stylet 20 and the desired feedback forthe operator. As with the actual tension limiting member 64, it will berecognized that numerous combinations and arrangements can be utilizedto accomplish the desired effect of psuedo-feedback mechanism 97.

[0050] In an embodiment directed to cardiac applications, increasing therelative tension force between the stylet wire 24 and the core wire 26causes the distal portion 30 of the stylet assembly 22 to bend until itultimately forms a J-shape as illustrated in FIG. 13. The amount ofcurvature of the stylet wire 24 can be increased and decreased asnecessary to traverse a body lumen or position the intravascular device50 in a desired location. The curve of the J-shape that the distalportion 40 of stylet assembly 22 can assume when the sliding mechanism64 is activated is preferably at least 180° and up to a 190° bend in aradius of less than 0.8″ in response to a relative tension of about 3.5lbs. FIG. 15 illustrates how the steerable stylet 20 of the presentinvention can be bent to allow for precise placement of a medical devicesuch as a cardiac lead 50 in a patient's right atrium. FIG. 14illustrates the stylet assembly 22 of the present invention within amedical lead 50 inside of a patient's vascular system 56.

[0051] Modeling of the stress levels at the distal end of the styletwire have indicated that high stress levels are reached early on whenbending of the distal region first occurs, remain relatively constantthrough the bending function, and then rise again when the maximumdesign radius is achieved. The actual stress is a combination of loadstress when the core wire applies force to the stylet wire and beamstress while the stylet assembly is passing through the bend radius.

[0052] To insure that the stylet 20 and intravascular device 50effectively return to an original or home position, the steerable stylet20 of a preferred embodiment arcs up to 15° in an opposite directionfrom the J-shape when the relative tension force is removed between thestylet wire 24 and the core wire 26. Preferably, this counter-arcing iscreated due to the beam strength of the stylet wire 24. Thecounter-arcing overshoots the neutral home position after which the homeposition is obtained as the stylet wire relaxes. As a result, thesteerable stylet 20 is more likely to ultimately return to a neutralhome position after being repeatedly flexed.

[0053]FIGS. 6 and 7 present a perspective and side view, respectively,of another embodiment of the manipulative handle 28 of the presentinvention in which relative tension force is applied to the styletassembly 22 by twisting a rear portion 72 of the handle housing 70 inrelation to the front portion 74 of the handle 70. Alternatively, arotatable collar or similar arrangement could be mounted on the handle70 to accomplish the same function. The rotational force is translatedby a screw or other mechanism into a longitudinal force to create therelative tension force that will separate the core wire 26 from thestylet wire 24.

[0054]FIGS. 8, 9, and 10 show a perspective, top, and side view,respectively, of yet another embodiment of the manipulative handle 28 ofthe present invention. The relative tension force is applied to the corewire 26 by pulling or pushing a pair of finger holds 82 and 84 inrelation to the manipulative handle housing 80. The finger holds 82 and84 are positioned on opposite sides of a middle portion 86 of thehousing 80 which preferably includes an additional thumb hold 88 that isnot moveable so as to allow for single handed operation of the steerablestylet 20.

[0055] Turning to FIGS. 11 and 12, they illustrate the notches 38 in thedistal region 36 of the stylet wire 24. The notches 38 alter thestrength of the wall of the stylet wire 24 in the distal region 36 thatallows the stylet wire 24 to more easily bend when the relative tensionforce is applied between the stylet wire 24 and the core wire 26.Preferably, notches or slots 38 are created by an electrical dischargemachine (EDM) process. Alternatively, the notches 38 may be created bycutting, laser, or water processes to remove the desired material of thestylet wire from the notches 38. The shape of the notches 38 ispreferably a rounded bottom channel, although other shapes such as aV-shape or a rectangular shape are also contemplated. In anotherembodiment, the effect of notches 38 could be achieved by selectivelyremoving portions of material from the wall of stylet wire 24 at thelocation similar to the locations of notches 38 and replacing theremoved material with a softer material. In still another embodiment,additional material could be added to the wall of stylet wire 24 atlocations generally radially opposite of the region where a curve isdesired to create a radially differential strength in the wall structureof stylet wire 24 that would encourage bending of the stylet wire 24 atthat region.

[0056] Spacing of the notches 38 will aid in determining the diameter ofthe J-shape that can be created by the distal region 36 of the styletwire 24. Notches 38 that are spaced farther apart will create a largerdiameter J-shape. Notches 38 that are spaced closer together will createa smaller diameter J-shape. The width of each notch 38 is critical to beable to position the slots closely without over-scoring the back of thetubular stylet wire 24.

[0057] In a preferred embodiment, the stylet wire 24 includes a seriesof at least ten notches 38 defined along the distal region 36 of thestylet wire 24. In one embodiment, at least a portion of the notches 38have a progressively decreasing depth distally to proximally along theseries as shown best in FIG. 12. Preferably, the portion of the notches38 that have a progressively decreasing depth is between 5% and 50% ofsaid series and will depend upon the desired application for thesteerable stylet 20 and the particular J-shape configuration to beobtained by operation of the steerable stylet 20. Preferably, at leastthree of the most proximal notches of the series have a progressivelydecreasing depth with a constant decrease in depth between adjacentnotches. In one embodiment, the portion of the notches 38 having aprogressively decreasing depth has a constant decrease in depth betweenadjacent notches. In a preferred embodiment, this constant decrease is20% between adjacent notches. In an alternative embodiment, theprogressively decreasing depths are not constant and may be selectedalong with alternate spacings between the notches 38 to achievealternate shapes of the distal end other than a simple J-shape.

[0058] Preferably, the distal region 36 is defined beginning between0.050 inches and 1.000 inches proximal to the distal end of the styletwire 24 and includes at least twenty notches 38 of between 0.005 inchesand 0.015 inches longitudinal width. A spacing between adjacent notchesis between 0.010 inches and 0.050 inches. A depth of at least ten of themost distal notches 38 of the series is preferably approximately equalto a radius of the stylet wire 24 minus a wall thickness of the styletwire. It has been found that this depth provides for maximum bendingstiffness in this application.

[0059] In another embodiment as shown in FIGS. 22 and 23, a styletassembly particularly adapted for neurological uses is presented. Inanother embodiment, a longitudinal tip of distal end portion 40 of corewire 26 includes a bulbous tip portion 110 having an outer diametersimilar to the outer diameter of stylet wire 24 that extends beyonddistal end portion 36 of stylet wire 24. In this embodiment, chamfers112 are created at the opening of the distal end portion 36 of styletwire 24 to seat the tip portion 110 of the core wire 26 in the openingand preferably an adhesive, such as an ultraviolet cured adhesive or anacrylate adhesive or the like, is used to secure the two wires together.In a preferred embodiment, the stylet wire is a tubular wire having anouter diameter of 0.013 inches and an inner diameter of 0.008 inches.The core wire 26 is created by starting with a solid core wire of 0.013inches and center grinding the wire to an outer diameter of 0.007 inchesexcept for the tip portion 110, which remains at an outer diameter of0.013 inches and is preferably rounded on the exterior. In thisembodiment, a polymer sheath is not utilized to keep the outer diameteras small as possible. It will be understood that the selection on innerand outer diameters of the stylet wire 24 are critical in being able tomaintain the desired beam strength and that these selections will dependupon numerous factors, including the materials used for both the styletwire and the core wire, and the nature and character of any notches 38to be defined in the stylet wire. This embodiment includes 28 totalnotches 38 spaced at 0.030″ with the first notch located 0.035″ from thedistal end portion 36 of the stylet wire 24. Preferably, the styletassembly 22 of this embodiment is capable of deflecting at least 45degrees and preferably up to 90 degrees in response to a relativetension force of about 8 lbs when deflected in a urethane lead.

[0060] In this embodiment, the stylet wire 24 can include two or moreseries of notches 38 that are created in the distal region 36 as shown,for example at 120 and 122. The spacing and dimension of the notches 38in first series 120 located more distally and the second series 122located more proximally are chosen in this example to cause the styletassembly 22 to first bend proximate the first series 120 in response torelative tension between the core wire 26 and the stylet wire 24 andthen make a second bend proximate the second series 120 in response to afurther increase in the relative tension. In this way, sigmoidal andcompound curves can be created. Additionally, by altering the radialorientation of the notches 38 as shown in FIG. 22, it is possible tocreate sigmoidal and compound curves in different planes. These featuresare very desirable for many neurological applications where thevascularture is more tortuous than in cardiac applications.

[0061] Referring to FIGS. 24 and 25, the calculations for creating thenotches 38 of a preferred embodiment will be described. For notches 38of maximum depth, the cuts should be made to a depth that is equal tothe thickness of the wall of stylet wire 24 and preferably the wallthickness ranges between 0.003 and 0.006 inches and the correspondinginner diameter ranges between 0.004 and 0.010 inches.

[0062] Referring to FIGS. 24 and 25, the calculations for determiningthe depth and distribution of notches 38 of a preferred embodiment willbe described. For maximum curvature of the stylet wire 24, the cutsshould be made to a depth equal to the thickness of the wall of thestylet wire and preferably the wall thickness ranges between 0.003 and0.006 inches and the corresponding inner diameter ranges between 0.004and 0.010 inches. The number of notches 38 determines the maximum angleof deflection of the stylet wire 24. The width of the notches 38determines the maximum amount of bending of the stylet wire 24.

[0063] A critical property of solid bodies and areas is the moment ofinertia. Moments of inertia are used in calculating the strength ofbeams, such as the stylet wire 24 of the present invention. Formulas arederived by multiplying basic particles of mass or area by the squares oftheir respective distances from the reference axis. Therefore, momentsof inertia are dependent upon the location of their axis. Moments ofinertia of plane area, where I is in the plane of the area are derivedfrom equations for calculating deflective stresses in beams. Theseformulas have been employed to design the stylet to deflect to thedesired positions while maintaining, but not exceeding the maximumallowable stresses under this desired deflection.

[0064] The following equations are used to determine the moments ofinertia that, in turn, are used to determine the beam strength of thestylet wire 24: $\begin{matrix}{A = {\frac{{Ro}^{2}}{2}\left( {{2\quad \alpha} - {\sin \quad 2\quad \alpha}} \right)}} & \left( {{eq}.\quad 1} \right) \\{I_{x} = {\frac{{ARo}^{2}}{4}\left\lbrack {I + \frac{2\quad \sin^{3}\quad \alpha \quad \cos \quad \alpha}{\alpha - {\sin \quad \alpha \quad \cos \quad \alpha}}} \right\rbrack}} & \left( {{eq}.\quad 2} \right) \\{I_{y} = {\frac{{ARo}^{2}}{4}\left\lbrack {I - {\frac{2}{3}\left( \frac{\sin^{3}\quad \alpha \quad \cos \quad \alpha}{\alpha \quad \sin \quad \alpha \quad \cos \quad \alpha} \right)}} \right\rbrack}} & \left( {{eq}.\quad 3} \right)\end{matrix}$

[0065] Where I_(x) and I_(y) represent the moments of inertia in the xand y plnaes; A represents the cross sectional area of the stylet wire24 at the cut; Ro represents the outside diameter of the stylet wire; rrepresents the inside diameter of the stylet wire; α represents theangle formed between the two radii extending from the center of thestylet wire to the edge of the cut.

[0066] As many different embodiments of the present invention can bemade without departing from the spirit and scope thereof, it is to beunderstood that the invention is not limited to the specific embodimentsthereof except as defined in the following claims.

What is claimed:
 1. A steerable stylet for use within a lumen of anintravascular device comprising: a stylet assembly having a distal endportion and a proximal end portion, said stylet assembly including: astylet wire having a lumen defined therein, said stylet wire having anouter diameter of less than 0.016 inches and a beam strength of at least0.005 lbf as measured by the ASTM E855-90 3-point bend test; and a corewire positioned within said lumen of said stylet wire and having adistal end portion of said core wire operably secured to said styletwire proximate a distal end portion of said stylet wire; and a handleproximate said proximal end portion of said stylet assembly, said handleincluding: a hand-held housing structure operably connected to one of aproximal end portion of said stylet wire and a proximal end portion ofsaid core wire; an adjustable tensioner mechanism operably connected tothe other of said proximal end portion of said stylet wire and saidproximal end portion of said core wire to adjust a relative tensionforce applied between said stylet wire and said core wire; and a tensionlimiter operably arranged to limit said tension force applied betweensaid core wire and said stylet wire to a limit force that is less than abreaking stress force of said stylet wire when said stylet assembly ispositioned within said lumen of said intravascular device.
 2. Thesteerable stylet of claim 1 wherein said breaking stress force of saidstylet wire is at least six pounds and said limit force of said tensionlimiter is less than four pounds.
 3. The steerable stylet of claim 1wherein said adjustable tensioner mechanism operably engages with aseparate compressible member to increase a force opposing movement ofsaid adjustable tensioner mechanism so as to provide tactile feedback toan operator that is generally indicative of said relative tension force.4. The steerable stylet of claim 1 wherein said beam strength of saidstylet wire is sufficient to cause said stylet wire to return to atleast an original position of said stylet wire as said relative tensionforce is removed from said stylet wire.
 5. The steerable stylet of claim1 wherein said stylet wire includes a series of at least ten notchesdefined along a distal region of said stylet wire.
 6. The steerablestylet of claim 5 wherein said series of a least ten notches includes atleast a portion of said notches having a progressively decreasing depthdistally to proximally along said series.
 7. The steerable stylet ofclaim 6 wherein said portion of said notches having said progressivelydecreasing depth comprises between five percent and fifty percent ofsaid series.
 8. The steerable stylet of claim 6 wherein each of saidnotches in said portion of said notches having said progressivelydecreasing depth has a constant decrease in depth between adjacentnotches.
 9. The steerable stylet of claim 5 wherein said distal regionis defined beginning between 0.050 inches and 1.000 inches proximal tosaid distal end of said stylet wire and includes at least twenty notchesof between 0.005 inches and 0.015 inches longitudinal width with aspacing between adjacent notches of between 0.010 inches and 0.050inches and a depth of at least ten of the most distal notches of saidseries being approximately equal to a radius of said stylet wire minus awall thickness of said stylet wire.
 10. The steerable stylet of claim 5wherein at least three of the most proximal notches of said series havea progressively decreasing depth with a constant decrease in depthbetween adjacent notches.
 11. The steerable stylet of claim 1 whereinsaid stylet wire includes a plurality of separate sets of notchesdefined along a distal region of said stylet wire.
 12. The steerablestylet of claim 11 wherein each set of notches is spaced apart from oneanother by at least 0.1 inches and each set of notches includes at leasta plurality of notches having a longitudinal width of between 0.005inches and 0.015 inches with a spacing between adjacent notches ofbetween 0.010 inches and 0.050 inches.
 13. The steerable stylet of claim11 wherein at least one of said sets of notches includes at least aportion of said notches having a progressively decreasing depth distallyto proximally along said series.
 14. The steerable stylet of claim 11wherein at least two of said sets of notches have different radialorientations of said notches such that the stylet assembly createscurves in two separate planes in response to said relative tensionforce.
 15. The steerable stylet of claim 11 wherein at least two of saidsets of notches have different spacings and widths of said notches suchthat the stylet assembly creates curves at two different times inresponse to said relative tension force.
 16. The steerable stylet ofclaim 1 wherein said proximal end portion of said core wire is fixedlyconnected to said housing structure, said proximal end portion of saidstylet wire is fixedly connected to said adjustable tensioner mechanismand said tension limiter has a first end portion fixedly connected tosaid housing structure and a second end portion operably connected tosaid adjustable tensioner mechanism.
 17. The steerable stylet of claim16 wherein said tension limiter is comprised of a constant force springwith a maximum tensile retention force less than the breaking stressforce of said stylet wire.
 18. The steerable stylet of claim 1 whereinsaid tension limiter is comprised of a spring with a maximum compressiveretention force less than the breaking stress force of said stylet wire.19. The steerable stylet of claim 1 wherein said tension limiter iscomprised of an elastomer with a maximum compressive retention forceless than the breaking stress force of said stylet wire.
 20. Thesteerable stylet of claim 1 wherein said distal end portion of said corewire is operably secured to said distal end portion of said stylet wirewithout annealing either of said distal end portions.
 21. A steerablestylet for use within a lumen of an intravascular device comprising: astylet wire having a distal end portion, a proximal end portion and alumen defined in said stylet wire, said stylet wire having an outerdiameter of less than 0.016 inches and a beam strength of at least 0.005lbf as measured by the ASTM E855-90 3-point bend test; a core wirehaving a distal end portion and a proximal end portion, said core wirepositioned within said lumen of said stylet wire and having said distalend portion of said core wire operably secured to said stylet wireproximate said distal end portion of said stylet wire; and a handleproximate said proximal end portion of said stylet wire, said handleincluding a hand-held housing structure having: means for adjusting arelative tension force applied between said stylet wire and said corewire; and means for limiting said relative tension force to a limitforce that is less than a breaking stress force of said stylet wire whensaid stylet wire is positioned within said lumen of said intravasculardevice.
 22. The steerable stylet of claim 21 wherein said breakingstress force of said stylet wire is at least six pounds and said limitforce of said tension limiter is less than four pounds.
 23. Thesteerable stylet of claim 21 wherein said handle further includes meansfor providing tactile psuedo-feedback to an operator that is generallyindicative of said relative tension force.
 24. The steerable stylet ofclaim 21 wherein said beam strength of said stylet wire is sufficient tocause said stylet wire to return to at least an original position ofsaid stylet wire as said relative tension force is removed from saidstylet wire.
 25. The steerable stylet of claim 21 wherein said styletwire includes at least one means for altering a wall strength of saidstylet wire along a distal region of said stylet wire.
 26. The steerablestylet of claim 25 wherein said means for altering the wall strengthcreates a radially differential wall strength between generally opposingwalls of said stylet wire.
 27. The steerable stylet of claim 25 whereinsaid means for altering the wall strength is selected from the setconsisting of: means for removing material at a series of locationsalong said stylet wire, means for adding material at a series oflocations along said stylet wire, or any combination thereof.
 28. Thesteerable stylet of claim 25 wherein said means for altering the wallstrength comprises a series of means for altering a materialcharacteristic of a wall of said stylet wire located along a portion ofsaid stylet wire.
 29. The steerable stylet of claim 28 wherein each ofsaid means for altering a material characteristic of said wall in saidportion have differing characteristics between adjacent means.
 30. Thesteerable stylet of claim 28 comprising a plurality of said means foraltering the wall strength, each said means for altering the wallstrength being spaced apart from one another by at least 0.1 inches. 31.The steerable stylet of claim 30 wherein at least two of said means foraltering the wall strength have different radial orientations of saidseries of means for altering the material characteristic such that thestylet assembly creates curves in two separate planes in response tosaid relative tension force.
 32. The steerable stylet of claim 30wherein at least two of said series of means for altering the materialcharacteristic have different spacings and widths such that the styletassembly creates curves at two different times in response to saidrelative tension force.
 33. The steerable stylet of claim 21 whereinsaid distal end portion of said core wire is operably secured to saiddistal end portion of said stylet wire by means for adhering withoutannealing either of said distal end portions.
 34. A method of steering astylet within a lumen of an intravascular device comprising: providing asteerable stylet including: a stylet assembly having a distal endportion and a proximal end portion, said stylet assembly including astylet wire having a lumen defined therein, said stylet wire having anouter diameter of less than 0.016 inches and a beam strength of at least0.005 lbf as measured by the ASTM E855-90 3-point bend test, and a corewire positioned within said lumen of said stylet wire and having adistal end portion of said core wire operably secured to said styletwire proximate a distal end portion of said stylet wire; and a handleoperably connected to said stylet wire proximate said proximal endportion of said stylet assembly, said handle including a hand-heldhousing structure, a tension adjuster and a tension limiter; insertingat least a portion of said stylet assembly into said lumen of saidintravascular device; and selectively deflecting a distal end portion ofsaid intravascular device by using said tension adjuster to adjust arelative tension force applied between said stylet wire and said corewire in such a manner that said tension limiter limits said relativetension force to a limit force that is less than a breaking stress forceof said stylet wire.
 35. The method of claim 34 wherein the step ofselectively deflecting deflects said distal end portion of saidintravascular device to a maximum deflection of at least 180 degreesfrom an original position of said distal end portion of saidintravascular device at a bend radius of less than an inch.
 36. Themethod of claim 34 wherein the step of selectively deflecting deflectssaid distal end portion of said intravascular device to a maximumdeflection of at least 45 degrees from an original position of saiddistal end portion of said intravascular device at a bend radius of lessthan an inch.
 37. The method of claim 34 further comprising: returningsaid distal end portion of said intravascular device to at least anoriginal position of said distal end portion of said intravasculardevice by releasing said relative tension force applied between saidstylet wire and said core wire and using said beam strength of saidstylet wire to cause said stylet wire to return to a position beyond anoriginal position of said stylet wire.
 38. The method of claim 34wherein said step of selectively deflecting is repeated at least fiftytimes without inducing stress or fatigue failure in said stylet wire.39. The method of claim 34 wherein said stylet assembly includes aplurality of regions along said distal end portion having differing wallstrengths such that the step of selectively deflecting creates acompound curve of said distal end portion.
 40. The method of claim 39wherein at least two of said plurality of regions are radially offsetwith respect to each other and the step of selectively deflectingcreates curves in at least two different planes.
 41. The method of claim39 where at least two of said plurality of regions having differingcharacteristics and the step of selectively deflecting creates curves attwo different times.
 42. A steerable stylet for use within a lumen of anintravascular device comprising: a stylet assembly having a distal endportion and a proximal end portion, said stylet assembly including: astylet wire having a lumen defined therein, said stylet wire having anouter diameter of less than 0.016 inches and a beam strength of at least0.005 lbf as measured by the ASTM E855-90 3-point bend test, said styletwire includes a series of at least ten notches defined along at leastone distal region of said stylet wire; and a core wire positioned withinsaid lumen of said stylet wire and having a distal end portion of saidcore wire operably secured to said stylet wire proximate a distal endportion of said stylet wire; and a handle proximate said proximal endportion of said stylet assembly, said handle including a hand-heldhousing structure having means for adjusting a relative tension forceapplied between said stylet wire and said core wire.
 43. The steerablestylet of claim 42 wherein said series of a least ten notches includesat least a portion of said notches having a progressively decreasingdepth distally to proximally along said series.
 44. The steerable styletof claim 43 wherein said portion of said notches having saidprogressively decreasing depth comprises between five percent and fiftypercent of said series.
 45. The steerable stylet of claim 43 whereineach of said notches in said portion of said notches having saidprogressively decreasing depth has a constant decrease in depth betweenadjacent notches.
 46. The steerable stylet of claim 42 wherein saiddistal region is defined beginning between 0.050 inches and 1.000 inchesproximal to said distal end of said stylet wire and includes at leasttwenty-five notches of between 0.005 inches and 0.015 incheslongitudinal width with a spacing between adjacent notches of between0.010 inches and 0.050 inches and a depth of at least ten of the mostdistal notches of said series being approximately equal to a radius ofsaid stylet wire minus a wall thickness of said stylet wire.
 47. Thesteerable stylet of claim 42 wherein at least three of the most proximalnotches of said series have a progressively decreasing depth with aconstant decrease in depth between adjacent notches.
 48. The steerablestylet of claim 42 wherein said stylet wire includes a plurality ofseparate sets of notches defined along a distal region of said styletwire.
 49. The steerable stylet of claim 48 wherein each set of notchesis spaced apart from one another by at least 0.1 inches and each set ofnotches includes at least a plurality of notches having a longitudinalwidth of between 0.005 inches and 0.015 inches with a spacing betweenadjacent notches of between 0.010 inches and 0.050 inches.
 50. Thesteerable stylet of claim 48 wherein at least one of said sets ofnotches includes at least a portion of said notches having aprogressively decreasing depth distally to proximally along said series.51. The steerable stylet of claim 48 wherein at least two of said setsof notches have different radial orientations of said notches such thatthe stylet assembly creates curves in two separate planes in response tosaid relative tension force.
 52. The steerable stylet of claim 48wherein at least two of said sets of notches have different spacings andwidths of said notches such that the stylet assembly creates curves attwo different times in response to said relative tension force.
 53. Thesteerable stylet of claim 42 wherein said distal end portion of saidcore wire is operably secured to said distal end portion of said styletwire without annealing either of said distal end portions.
 54. Asteerable stylet for use within a lumen of an intravascular devicecomprising: a stylet assembly having a distal end portion and a proximalend portion, said stylet assembly including: a stylet wire having alumen defined therein, said stylet wire having an outer diameter of lessthan 0.016 inches and a beam strength of at least 0.005 lbf as measuredby the ASTM E855-90 3-point bend test, said stylet wire includes aseries of means for altering a material characteristic of a wall of saidstylet wire located along a portion of said stylet wire; and a core wirepositioned within said lumen of said stylet wire and having a distal endportion of said core wire operably secured to said stylet wire proximatea distal end portion of said stylet wire; and a handle proximate saidproximal end portion of said stylet assembly, said handle including ahand-held housing structure having means for adjusting a relativetension force applied between said stylet wire and said core wire. 55.The steerable stylet of claim 54 wherein each of said means for alteringa material characteristic of said wall in said portion have differingcharacteristics between adjacent means.
 56. The steerable stylet ofclaim 54 comprising a plurality of said series of means, each of saidseries of means being spaced apart from one another by at least 0.1inches.
 57. The steerable stylet of claim 56 wherein at least two ofsaid series of means have different radial orientations such that thestylet assembly creates curves in two separate planes in response tosaid relative tension force.
 58. The steerable stylet of claim 56wherein at least two of said series of means have differentcharacteristics such that the stylet assembly creates curves at twodifferent times in response to said relative tension force.
 59. Thesteerable stylet of claim 54 wherein said distal end portion of saidcore wire is operably secured to said distal end portion of said styletwire by means for adhering without annealing either of said distal endportions.